It has recently been required that variable attenuators used in audio products have a large maximum attenuation characteristic. Many variable attenuators have a comparatively low total resistance of, for example, lower than 10 k.OMEGA., and it is now required that these attenuators be able to produce a maximum attenuation in the order of -100 dB to -120 dB.
A variable attenuator generally consists of a resistance element having conductive members typically made of a silver paste provided at the respective end portions of the resistance element. Terminals are secured to the conductive members, and a sliding member connected electrically to a tap terminal is slidingly movable along the resistance element. In such a variable attenuator, a sliding member is moved along the resistance element while a voltage is applied between the two terminals, so as to extract an attenuation voltage in accordance with the amount of movement of the sliding member. However, even when the sliding member is moved to the end portion of its path, a slight amount of voltage usually occurs across the sliding member due to a resistance existing in those portions of the conductive members that are between the end portion of the sliding members and the terminals secured to the conductive members. This offers an obstruction to the improvement of maximum attenuation amount in a variable attenuator having a comparatively low total resistance. For example, when the total resistance is 10 k.OMEGA., with the resistance in the conductive members being 1.OMEGA., the maximum attenuation amount is normally about -80 dB (20 log 1/10000), which is far lower than the currently demanded value of -100 dB to -120 dB.
Therefore, an object of the present invention is to provide a variable attenuator which will be able to obtain a large maximum attenuation amount even when the attenuator has a low total resistance.
Another object of the present invention is to provide a variable attenuator having a simple construction and a large maximum attenuation amount.
Still another object of the present invention is to provide a variable attenuator, which can be easily manufactured at a low cost and which has a large attenuation amount.
A further object of the present invention is to provide a variable attenuator which is especially suitable for controlling the sound volume of audio devices.